1. Field of the Invention
The present invention relates to an electrophotographic copying machine. More particularly, the present invention relates to an electrophotographic copying machine which can form an electrostatic latent image of an additional information other than the original on a photosensitive member in addition to an electrostatic latent image corresponding to the original copy.
2. Description of the Prior Arts
The electrophotographic copying machine of this type was disclosed, for example, in Japanese Patent Publication No. 24785/1983 published on May 23, 1983, Japanese Patent Application Laid Open Nos. 74762/1982, 92247/1979 and 83834/1983 laid open for public inspection respectively on May 11, 1982, July 21, 1979 and May 19, 1983.
The electrophotographic copying machine disclosed in Japanese Patent Publication No. 24785/1983 is constructed in such way that the electrostatic latent image of the additional information other than the original copy image may be formed by the residual charge (350 V) gained by controlling the exposure of the original copy image to one half of the electrified charge on the photosensitive drum, in other words, by controlling the potential of the region where the electrostatic latent image is not formed at 700 V and the region where the electrostatic latent image is formed at 350 V. However, in this prior art, a density of the image is not controllable, nearing that it is not available as a copying machine, except it may be as a printer.
Furthermore, in Japanese Patent Application Laid Open No. 74762/1982 there is disclosed only that the additional or secondary information other than the original copy image or a primary information can be formed but nothing about the definite solutions are disclosed.
In Japanese Patent Application Laid Open No. 92247/1979 an electrophotographic copying machine having a liquid crystal shutter which exposes the additional or secondary informations on the photosensitive drum and a shield means to prevent the projection of the exposed ray for the primary information in the region where the secondary information to be formed as the electrostatic latent image is disclosed. This prior art, however, is aimed to form the additional information by the liquid crystal shutter, accordingly it requires not only an additional light source but also would result in a complex construction.
Moreover, in Japanese Patent Application Laid Open No. 83834/1983, an electrophotographic copying machine using an LED array for the additional information is disclosed. However, there is nothing about the definite instruction on the material of the photosensitive drum in this cited publication. Accordingly, the definite realization of the electrophotographic copying machine experimented by the inventors and others according to the contents taught in Japanese Patent Application Laid Open No. 83834/1983 was impossible even by referring to the contents of Japanese Patent Application Laid Open No. 92247/1979.